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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
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    <title>Document</title>
    <style>
        .demo-wrapper {
            color: #f40;
        }
    </style>
</head>
<body>
    <div class="demo-wrapper">
        你好，浏览器
    </div>
    <script>
        let oDiv = document.querySelector('.demo-wrapper');
        console.log(oDiv)
        oDiv.addEventListener('click', function () {
            oDiv.classList.add('show');
        }, false)
    </script>
</body>
</html>